The project is aimed at contributing to our understanding of enzyme catalysis by providing information on the steric course of a number of enzyme reactions at prochiral and pro-prochiral centers. The work will involve the use of isolated enzymes and substrates labeled stereospecifically with tritium and/or deuterium followed, if necessary, by stereospecific degradations of the products. Enzyme reactions to be investigated are some steps of the shikimic acid pathway, a number of pyridoxal phosphate-catalyzed beta-replacement and elimination reactions, the transfer of methyl groups in biological C-, N-, O- and S- methylation reactions and the isoprenylation of an aromatic ring system.